Kawah Ijen
In Indonesia, there is a volcano that inexplicably spews blue lava. There are sulfuric gases that get released during an eruption, which then changes the color of the lava. The blue-colored flames meld into liquid sulfur. Technically, it's not lava and can be very toxic is anyone nearby who might have breathed it in.
The island of Java, where the blue volcano is located, is the 13th largest island in the world. The volcano remains active, but has not had a full, magmatic eruption since 1817. The blue lava still spills out from time to time and is generally an easy site to see.